In recent years, network traffics have been rapidly increased with the wide spread of the Internet and mobile networks. Therefore, in carrier core networks, there is an urgent need to expand transmission capacity and the introduction of the OTN (Optical Transport Network) which realizes the transmission capacity of 100 Gbps is underway. Moreover, expansion of transmission capacity of access networks using Ethernet® technology and IP (Internet Protocol) technology is progressing as well.
In addition, there have been known techniques for informing each device in a network of an alarm when a failure occurs in the network. There have been also known techniques in which two Ethernets are connected to an SDH (Synchronous Digital Hierarchy) network and, if a failure occurs in the Ethernet of one side, the Ethernet of one side is switched to the Ethernet of the other side.
Related technologies are disclosed in, for example, Japanese Laid-Open Patent Publication No. 05-30075 and International Publication Pamphlet No. WO2005-079015.